The present invention relates to a method and device for monitoring lubrication at contact points between structural elements movable relative to each other, separated from each other by a lubricant film and formed of different electrically-conductive materials. More particularly, this invention relates to a method and a device for monitoring lubrication points between a rotary shaft and a sleeve bearing.
In monitoring the points of bearing, particularly in the bearings of large machines, such as crank shaft bearings in lop-sided diesel motors it is very important that breaks in a lubrication film be determined before the beginning of damaging the bearing and countermeasures have been suggested to prevent damage to the bearing and the crank shaft and thereby the breakdown of the machine with usual damaging results.
It has been known to connect the shaft and the sleeve bearing in an electric circuit at that location of a lubricant, at which both components are in contact. Such a circuit has been provided with a voltage source and has been used to produce a current resistance as a signal issued when a break in a lubricant film occurs. The voltage source accommodated in an outer connection circuit has produced a current flowing in the circuit through the point of lubrication.
The disadvantage of this conventional monitoring of points of lubrication is that despite the fact that only brief metallic and therefore low-resistance contacts occur between the shaft and the bearing false alarm signals can take place.
These brief low-resistance contacts are noticable when many bearing points are sensed simultaneously. Lubrication oil which contains chemical agents has a certain conductivity whereby it is difficult to differentiate the conductivity of a direct metallic contact from the conductivity of the chemical agents of the oil. Since the circuit during the rotation of the shaft must be connected to the shaft by a wiper and the contact resistance on the wiper can fluctuate the monitoring process becomes more difficult.
It has been also known in a process of points of lubrication being monitored to determine temperatures of the bearings with various temperature sensors and to produce an alarm signal when the temperature has reached a non-permissible high value. Since such temperature sensors can determine only punctual temperatures and these feelers can not be precisely mounted at the enter surface of the bearing for structural reasons this has resulted in a delay in time unless a thermal flow has been transmitted from the spots of damage to the temperature feeler. This is particularly unfavorable when the spot of damage on the bearing is positioned remotely from the temperature sensors.